Screening for tyrosinase inhibitors among extracts of seashore plants and identification of potent inhibitors from Garcinia subelliptica

The tyrosinase inhibitory activity of methanol extracts of the leaves of 39 plant species growing on the seashore of Iriomote island (Okinawa, Japan) was investigated. The extracts of Hibiscus tiliaceus, Carex pumila, and Garcinia subelliptica showed potent activity among them. The inhibitors in the extract of Garcinia subelliptica were purified by assay-guided fractionation to give two biflavonoids. These were known compounds (2R,3S-5,7,4',5,7,3',4'-heptahydroxy flavanone[3-8] flavone and 5,7,4',5,7,3',4'-heptahydroxy[3-8] biflavanone), although their strong inhibitory activity toward tyrosinase is revealed for the first time in this work. One of these biflavonoids (2R,3S-5,7,4',5,7,3''', 4'-heptahydroxy flavanone[3-8] flavone) showed much stronger activity (IC50 2.5 proportional tom) than that of kojic acid (IC50 9.1 proportional tom) when L-tyrosine was used as the substrate.